Christopher Tenhoor

Successful conversion from conventional immunosuppression to anti-CD154 monoclonal antibody costimulatory molecule blockade in rhesus renal allograft recipients.

BACKGROUND Several conventional forms of immunosuppression have been shown to antagonize the efficacy of anti-CD154 monoclonal antibody- (mAb) based costimulatory molecule blockade immunotherapy. Our objective was to determine if allograft recipients treated with a conventional immunosuppressive regimen could be sequentially converted to anti-CD154 mAb monotherapy without compromising graft survival. METHODS Outbred juvenile rhesus monkeys underwent renal allotransplantation from MHC-disparate donors. After a 60-day course of triple therapy immunosuppression with steroids, cyclosporine, and mycophenolate mofetil, monkeys were treated with: (1) cessation of all immunosuppression (control); (2) seven monthly doses of 20 mg/kg hu5C8 (maintenance), or; (3) 20 mg/kg hu5C8 on posttransplant days 60, 61, 64, 71, 79, and 88 followed by five monthly doses (induction+maintenance). Graft rejection was defined by elevation in serum creatinine>1.5 mg/dl combined with histologic evidence of rejection. RESULTS Graft survival for the three groups were as follows: group 1 (control): 70, 75, >279 days; group 2 (maintenance): 83, 349, >293 days, and; group 3 (induction+maintenance): 355, >377, >314 days. Acute rejection developing in two of four monkeys after treatment with conventional immunosuppression was successfully reversed with intensive hu5C8 monotherapy. CONCLUSIONS Renal allograft recipients can be successfully converted to CD154 blockade monotherapy after 60 days of conventional immunosuppression. An induction phase of anti-CD154 mAb appears to be necessary for optimal conversion. Therefore, although concurrent administration of conventional immunosuppressive agents including steroids and calcineurin inhibitors has been shown to inhibit the efficacy of CD154 blockade, sequential conversion from these agents to CD154 blockade appears to be effective.

Pharmacokinetics, biologic activity, and tolerability of alefacept by intravenous and intramuscular administration

Alefacept, human LFA-3/IgG1 fusion protein, is currently under clinical development for the treatment of chronic plaque psoriasis and other T cell mediated disorders. This recombinant protein binds CD2 on T cells and Fcγ RIII on accessory cells (e.g., natural killer cells, macrophages), inhibiting T cell activation/proliferation and inducing selective T cell apoptosis. These effects are associated with selective reductions in memory-effector (CD4+CD45RO+; and CD8+CD45RO+) T cells. Two open-label studies were conducted in healthy male volunteers to evaluate the pharmacokinetics, biologic activity, and tolerability of a single dose of alefacept when administered as a 0.15 mg/kg 30-sec i.v. bolus (n=12), 0.04 mg/kg intramuscular (i.m.) injection (n=8), or 0.04 mg/kg 30-min intravenous (i.v.) infusion (n=8). I.V. infusion pro- duced a higher Cmax(0.96±0.26 mcg/ml vs. 0.36±0.19 mcg/ml) and a shorter Tmax(2.8±1.9 hr vs. 86±60 hr) when compared to i.m. injection. Based on AUC0-last and AUC0-∞ values, the relative bioavailability of i.m. to i.v. infusion was approximately 60%. After absorption from the i.m. injection was complete, the rate of alefacept elimination from the serum appeared consistent with the i.v. infusion half-life (approximately 12 days). Biologic activity was demonstrated by transient reductions in absolute number of CD2+ lymphocytes, with notable specificity for memory T-cell subsets. Alefacept was well tolerated; the most common adverse effects were headache, pharyngitis, rash, and myalgia. IM administration was not associated with significant local reactions. Results of these studies support i.v. bolus or i.m. administration of alefacept. An i.m. dose of approximately 150 to 200% of the i.v. dose is an appropriate and convenient alternative to i.v. administration.

Inhibiting Plasma Kallikrein for Hereditary Angioedema Prophylaxis

Background Hereditary angioedema with C1 inhibitor deficiency is characterized by recurrent, unpredictable swelling episodes caused by uncontrolled plasma kallikrein generation and excessive bradykinin release resulting from cleavage of high‐molecular‐weight kininogen. Lanadelumab (DX‐2930) is a new kallikrein inhibitor with the potential for prophylactic treatment of hereditary angioedema with C1 inhibitor deficiency. Methods We conducted a phase 1b, multicenter, double‐blind, placebo‐controlled, multiple‐ascending‐dose trial. Patients with hereditary angioedema with C1 inhibitor deficiency were randomly assigned in a 2:1 ratio to receive either lanadelumab (24 patients) or placebo (13 patients), in two administrations 14 days apart. Patients assigned to lanadelumab were enrolled in sequential dose groups: total dose of 30 mg (4 patients), 100 mg (4 patients), 300 mg (5 patients), or 400 mg (11 patients). The pharmacodynamic profile of lanadelumab was assessed by measurement of plasma levels of cleaved high‐molecular‐weight kininogen, and efficacy was assessed by the rate of attacks of angioedema during a prespecified period (day 8 to day 50) in the 300‐mg and 400‐mg groups as compared with the placebo group. Results No discontinuations occurred because of adverse events, serious adverse events, or deaths in patients who received lanadelumab. The most common adverse events that emerged during treatment were attacks of angioedema, injection‐site pain, and headache. Dose‐proportional increases in serum concentrations of lanadelumab were observed; the mean elimination half‐life was approximately 2 weeks. Lanadelumab at a dose of 300 mg or 400 mg reduced cleavage of high‐molecular‐weight kininogen in plasma from patients with hereditary angioedema with C1 inhibitor deficiency to levels approaching that from patients without the disorder. From day 8 to day 50, the 300‐mg and 400‐mg groups had 100% and 88% fewer attacks, respectively, than the placebo group. All patients in the 300‐mg group and 82% (9 of 11) in the 400‐mg group were attack‐free, as compared with 27% (3 of 11) in the placebo group. Conclusions In this small trial, administration of lanadelumab to patients with hereditary angioedema with C1 inhibitor deficiency reduced cleavage of high‐molecular‐weight kininogen and attacks of angioedema. (Funded by Dyax; ClinicalTrials.gov number, NCT02093923.)

Inhibition of plasma kallikrein by a highly specific active site blocking antibody.

Background: Unregulated plasma kallikrein proteolytic activity can result from C1-inhibitor deficiency, causing excessive and potentially fatal edema. Results: The antibody DX-2930 potently and specifically inhibits plasma kallikrein and exhibits a long plasma half-life. Conclusion: An antibody protease inhibitor can lead to potent and specific bioactivity. Significance: DX-2930 could be an effective therapeutic for the prophylactic inhibition of plasma kallikrein-mediated diseases. Plasma kallikrein (pKal) proteolytically cleaves high molecular weight kininogen to generate the potent vasodilator and the pro-inflammatory peptide, bradykinin. pKal activity is tightly regulated in healthy individuals by the serpin C1-inhibitor, but individuals with hereditary angioedema (HAE) are deficient in C1-inhibitor and consequently exhibit excessive bradykinin generation that in turn causes debilitating and potentially fatal swelling attacks. To develop a potential therapeutic agent for HAE and other pKal-mediated disorders, we used phage display to discover a fully human IgG1 monoclonal antibody (DX-2930) against pKal. In vitro experiments demonstrated that DX-2930 potently inhibits active pKal (Ki = 0.120 ± 0.005 nm) but does not target either the zymogen (prekallikrein) or any other serine protease tested. These findings are supported by a 2.1-Å resolution crystal structure of pKal complexed to a DX-2930 Fab construct, which establishes that the pKal active site is fully occluded by the antibody. DX-2930 injected subcutaneously into cynomolgus monkeys exhibited a long half-life (t½ ∼12.5 days) and blocked high molecular weight kininogen proteolysis in activated plasma in a dose- and time-dependent manner. Furthermore, subcutaneous DX-2930 reduced carrageenan-induced paw edema in rats. A potent and long acting inhibitor of pKal activity could be an effective treatment option for pKal-mediated diseases, such as HAE.

Structural basis for pH-insensitive inhibition of immunoglobulin G recycling by an anti-neonatal Fc receptor antibody.

The neonatal Fc receptor FcRn plays a critical role in the trafficking of IgGs across tissue barriers and in retaining high circulating concentrations of both IgG and albumin. Although generally beneficial from an immunological perspective in maintaining IgG populations, FcRn can contribute to the pathogenesis of autoimmune disorders when an abnormal immune response targets normal biological components. We previously described a monoclonal antibody (DX-2507) that binds to FcRn with high affinity at both neutral and acidic pH, prevents the simultaneous binding of IgG, and reduces circulating IgG levels in preclinical animal models. Here, we report a 2.5 Å resolution X-ray crystal structure of an FcRn–DX-2507 Fab complex, revealing a nearly complete overlap of the IgG–Fc binding site in FcRn by complementarity-determining regions in DX-2507. This overlap explains how DX-2507 blocks IgG binding to FcRn and thereby shortens IgG half-life by preventing IgGs from recycling back into circulation. Moreover, the complex structure explains how the DX-2507 interaction is pH-insensitive unlike normal Fc interactions and how serum albumin levels are unaffected by DX-2507 binding. These structural studies could inform antibody-based therapeutic approaches for limiting the effects of IgG-mediated autoimmune disease.